The present invention relates to magnetic materials and in particular to an alloy which when fully processed has a major portion of the grains exhibiting a (110)[001] orientation and is characterized by the grains having undergone a secondary recrystallization.
In the past, oriented electrical steels have been characterized usually by the addition of sufficient silicon to close the .gamma. loop to such an extent that heating a steel containing 3% silicon with sufficiently low carbon content to a temperature of about 1200.degree. C. resulted in heating said materials in the all .alpha. field, the loop having been restricted sufficiently that the alloy would avoid any phase transformation upon heating or cooling to such elevated temperatures.
Commensurate with the addition of 3% silicon to the underlying basic iron was the further factor for the necessity for the control of the manganese and sulfur contents such that a sufficient degree of manganese sulfide was required to be present in the alloy prior to the final high-temperature anneal. During such high-temperature anneal it was the function of the manganese sulfide to inhibit less favorably oriented grains in order to permit the grains having a (110)[001] orientation to grow at the expense of less favorably oriented grains. This occurred during heating of the material to the final high-temperature anneal.
However, once the desired orientation was obtained the sulfur content was no longer needed and, in fact, provided a deleterious effect on the overall magnetic characteristics such that in the commercial manufacture of oriented silicon steels, a sufficiently high temperature was obtained in the final anneal and held for a sufficiently long period of time to dissociate the manganese sulfide into its components and thereby through the use of a dry hydrogen atmosphere, the sulfur content was reduced to acceptably low levels so that the overall combination of magnetic characteristics obtainable in the steel was optimized.
In more recent years a new type of technology has been evolved which employs a different type of inhibitor, namely nitride or certain borides in combination with manganese sulfide utilized in the earlier produced oriented silicon steels. These steels in which the aluminum nitride or other inhibiting element was utilized have been known commercially as the so-called high-B steels. These high-B steels usually had an induction in excess of about 18.8 kilogauss at a magnetizing force of 10 oersted.
One common thread is apparent in these prior art steels and that is that the final heat treatment takes place near 1200.degree. C., a temperature in excess of the .alpha..revreaction..gamma. transformation temperature for materials containing, for example, less than about 2.5% silicon. Typical of the prior art in which the aluminum nitride was utilized as the inhibiting agent is U.S. Pat. No. 3,287,183 in the name of Taguchi et al. These inventors find that two cold rolling steps must be critically controlled, the first one being within the limitation of 5 to 40%, and the second one being within the range between 81 and 95% reduction in area. In addition, Taguchi et al. required a definite relationship between the sulfur and the acid soluble aluminum together with an intermediate annealing temperature range, none of which the applicants have found to be critical. In fact, applicants have substantially less sulfur and aluminum than recommended by Taguchi et al. and the temperature of their intermediate anneal is usually in the neighborhood of about 850.degree. C., whereas Taguchi et al. recommends 950.degree. to 1200.degree. C.
Another patnet to Sakakura et al. namely U.S. Pat. No. 3,632,456 describes essentially the same composition of matter and the processing which is fairly similar to Taguchi et al. and differing therefrom by requiring the annealing and quenching of the strip material in order to precipitate aluminum nitride. Sakakura et al. also find it necessary for forming a primary recrystallized microstructure in the steel sheet between cold rolling operations. To substantiate the same effect, more elucidation on the rolling schedules as well as the necessity for the precipitation of the aluminum nitride through a specified heat treatment may be found in U.S. Pat. No. 3,636,579 also in the name of Sakakura, et al.